replacing the default headers and/or footers for pages in a group (e.g., using (:noheader:) and or (:nofooter:) -- see PageDirectives).

To create a group header, just create a new page called YourGroup.GroupHeader. Group headers allow authors to create groups with custom headers and footers without having to coordinate with a wiki administrator.

The default GroupHeader or GroupFooter can be suppressed on an individual page (such as a group's HomePage) by using the (:nogroupheader:) and (:nogroupfooter:) markups on that page.

If a generic GroupHeader is used in one wikigroup (say, the Site wikigroup), then the code can be easily duplicated in the GroupHeader of any other group by using
(:include Site.GroupHeader:). See IncludeOtherPages.

If you want a header or footer to appear when you print a page (action print), simply create a page called YourGroup.GroupPrintHeader or YourGroup.GroupPrintFooter and fill it with your markup.

Note that single quotes must be used so that $Group (which is part of the default contents of $GroupHeaderFmt) will be substituted properly by PmWiki, and that this applies to all variables ending in $...Fmt.
See also the Cookbook:AllGroupHeader page.